This module implements labeled MVars. The interface is analogous
to Control.Concurrent.MVar, but the operations take place in
the LIO monad. Moreover, taking and putting MVars calls a write
guard wguard as every read implies a write and vice versa. This
module exports only the safe subset (non-TCB) of the LMVar module
trusted code can import LIO.Concurrent.LMVar.TCB.
The interface is documented in LIO.Concurrent.LMVar.TCB.